zig rc: Fix include directory detection when cross-compiling from certain host archs

Previously, resinator would use the host arch as the target arch when looking for windows-gnu include directories. However, Zig only thinks it can provide a libc for targets specified in the `std.zig.target.available_libcs` array, which only includes a few for windows-gnu. Therefore, when cross-compiling from a host architecture that doesn't have a windows-gnu target in the available_libcs list, resinator would fail to detect the MinGW include directories.

Now, the custom option `/:target` is passed to `zig rc` which is intended for the COFF object file target, but can be re-used for the include directory target as well. For the include directory target, resinator can get away with being a bit lossy in its conversion from coff.MachineType to Target.Cpu.Arch (to ensure that the target arch is within the set of available_libcs) since the include directories all resolve to `any-windows-any` in the end anyway (which is what Zig actually ships for MinGW).

Fixes the `windows_resources` standalone test failing when the host is, for example, `risc64-linux`.

Author: squeek502

lib/compiler/resinator/main.zig

@@ -104,7 +104,26 @@ pub fn main() !void {
     }
     const maybe_dependencies_list: ?*std.ArrayList([]const u8) = if (options.depfile_path != null) &dependencies_list else null;
 
-    const include_paths = getIncludePaths(arena, options.auto_includes, zig_lib_dir) catch |err| switch (err) {
+    // Use the COFF target to inform which architecture to target for the includes, too.
+    //
+    // Note: This is more of a "best fit" mapping to architectures that Zig recognizes
+    // and considers valid for providing a libc for. For the purposes of include directories,
+    // when targeting `gnu` the same set of headers will be used for each target arch so we're
+    // really just trying to avoid Zig thinking that it can't provide a libc for the target
+    // so we can get the path to the MinGW include directories shipped with Zig.
+    const includes_arch: std.Target.Cpu.Arch = switch (options.coff_options.target) {
+        .X64 => .x86_64,
+        .I386 => .x86,
+        .ARMNT => .thumb,
+        .ARM64 => .aarch64,
+        .ARM64EC => .aarch64,
+        .ARM64X => .aarch64,
+        .IA64 => .x86_64,
+        .EBC => .x86_64,
+        // the above cases are exhaustive of all the `MachineType`s supported (see supported_targets in cvtres.zig)
+        else => unreachable,
+    };
+    const include_paths = getIncludePaths(arena, options.auto_includes, zig_lib_dir, includes_arch) catch |err| switch (err) {
         error.OutOfMemory => |e| return e,
         else => |e| {
             switch (e) {
@@ -498,7 +517,7 @@ const IoStream = struct {
     };
 };
 
-fn getIncludePaths(arena: std.mem.Allocator, auto_includes_option: cli.Options.AutoIncludes, zig_lib_dir: []const u8) ![]const []const u8 {
+fn getIncludePaths(arena: std.mem.Allocator, auto_includes_option: cli.Options.AutoIncludes, zig_lib_dir: []const u8, target_arch: std.Target.Cpu.Arch) ![]const []const u8 {
     var includes = auto_includes_option;
     if (builtin.target.os.tag != .windows) {
         switch (includes) {
@@ -521,6 +540,7 @@ fn getIncludePaths(arena: std.mem.Allocator, auto_includes_option: cli.Options.A
 
                 const target_query: std.Target.Query = .{
                     .os_tag = .windows,
+                    .cpu_arch = target_arch,
                     .abi = .msvc,
                 };
                 const target = std.zig.resolveTargetQueryOrFatal(target_query);
@@ -546,6 +566,7 @@ fn getIncludePaths(arena: std.mem.Allocator, auto_includes_option: cli.Options.A
             .gnu => {
                 const target_query: std.Target.Query = .{
                     .os_tag = .windows,
+                    .cpu_arch = target_arch,
                     .abi = .gnu,
                 };
                 const target = std.zig.resolveTargetQueryOrFatal(target_query);

src/Compilation.zig

@@ -6058,6 +6058,7 @@ fn updateWin32Resource(comp: *Compilation, win32_resource: *Win32Resource, win32
                 self_exe_path,
                 "rc",
                 "--zig-integration",
+                // Note: Don't need to pass target here since no preprocessing is done
                 "/:no-preprocess",
                 "/x", // ignore INCLUDE environment variable
                 "/c65001", // UTF-8 codepage
@@ -6115,6 +6116,8 @@ fn updateWin32Resource(comp: *Compilation, win32_resource: *Win32Resource, win32
             self_exe_path,
             "rc",
             "--zig-integration",
+            "/:target",
+            @tagName(comp.getTarget().cpu.arch),
             "/:depfile",
             out_dep_path,
             "/:depfile-fmt",